1. Field of the Invention
The present invention relates to a method and machine for forming cardboard, corrugated cardboard or similar sheet material cases, having a polygonal section and particularly a square or rectangular section.
2. Description of the Prior Art.
Cases of this type are formed from a single blank of said sheet material, comprising an assembly of panels (at least three) connected together by parallel fold-lines and provided laterally with flaps, connected respectively to said panels by fold-lines perpendicular to the fold-lines connecting said panels together and intended to form the bottom and the lid of said cases. The free edge of one of the endmost panels of said assembly is provided with a tongue connected to said endmost panel by a fold-line parallel to those connecting said panels together and intended to be fixed against the free edge of the opposite endmost panel.
Known cases of this type are called "American" and they have a square or rectangular section (transversely to said boards). They are manufactured by an industrial cardboard maker who, from said blank forms a flattened tubular blank by folding said blank about the median fold-line of said assembly of panels and fixing said tongue to the opposite endmost panel. At that time, said model has then a section in the form of a flattened parallelogram, said lateral flaps extending the corresponding panels respectively outwardly. Then, these flattened blanks are delivered to the user who, in order to house therein objects to be packed, puts them into shape by expansion parallel to the flattened diagonal of said parallelogram then folds back and glues said flaps so as to form the bottom and, after filling, the lid of said case.
Such a procedure for manufacturing and use has numerous drawbacks; In fact:
of course, both manufacture of the flattened blank by the cardboard maker and the shaping of said blanks by the user are achieved by means of automatic machines. It can then be seen that it is necessary to use two complex and so expensive automatic machines, which adds to the cost of using said cases.
bacause of the lateral flaps, it is difficult to strictly guide the edges of the blank at the moment of fixing the tongue on the opposite endmost panel, so that squaring is poor and the bonding line obtained is not strictly parallel to the fold-lines joining said flaps together; the section of the case is therefore not strictly identical between the bottom and the lid and the result is defects in the presentation of the cases, which adversely affects the quality thereof.
the flattened blanks have an extra thickness in the middle since the flattened blank comprises locally three thicknesses instead of two. This extra thickness results in unbalancing the stacks of blanks formed for storage and transporting said blanks. The result is difficulties in handling said stacks.
because of the above mentioned extra thicknesses, the number of flattened blanks which can be housed in the feed magazine of the shaping and filling machine on the user's premises is limited.
the intermediate fold-lines of the panels are bent to a maximum during formation of the flattened blanks; in addition, the intermediate fold-lines form external edges of said blanks. Consequently, they are weakened by flattening the blanks and subject to external aggressions. The result is that these intermediate fold-lines form lines of lesser strength for said cases.
the boards of said cases are necessarily four in number and identical two by two,
because of inaccuracies in fixing and because the edges are made fragile, it is necessary to use high quality sheet material. The cost of said cases is therefore high.